1. Field of the Invention
The present invention relates to a control device for a four-wheel drive (All-Wheel-Drive) vehicle that has an electrically-driven parking brake for braking the rear wheels and freely distributes the driving force among the front and rear wheels.
2. Description of the Related Art
An electrically-driven parking brake which is actuated by an electrically-driven motor has been developed and practically used a sparking brakes for vehicles. JP-A-7-89420 discloses one of these electrically-driven parking brakes. According to JP-A-7-89420, the electrically-driven parking brake comprises a cylinder formed in a caliper, a freely-slidable piston disposed in the cylinder, a screw shaft for reciprocating the piston to a disc, a motor for actuating the screw shaft, a measuring mechanism that is provided to the screw shaft and controls the shift amount of the piston by brake press force occurring to the piston, and an electric control device for controlling the motor and the measuring mechanism.
Since the electrically-driven parking brake described in JP-A-7-89420 has a feature that it has a longer stop holding time as compared with a main brake using normal hydraulic pressure, and thus it can be applied to various vehicle control devices which have been recently practically used (for example, a preceding vehicle following control device, etc.). However, the electrically-driven parking brake brakes only the rear wheels, and thus the maximum generable braking force is low, so that the vehicle may be destabilized by the braking of only the rear wheels.